The present invention relates to an integrated air-separation/energy-generation process and to a plant for implementing such a process.
It is well known to send a nitrogen-enriched gas from an air separation unit upstream of a turbine for expanding combustion gas. The combustion chamber is fed with compressed air coming from an air compressor which may deliver all or some of the air needed for the air separation unit (ASU) as illustrated in EP-A-0 538 118. Alternatively, as in the case of GB-A-2 067 688, all the air may come from a dedicated compressor.
If it were desired to produce argon, EP-A-568 431 describes the use of an integrated system.
The difficulties in regulating this kind of system are explained in EP-A-0 622 595.
In general, for reasons of reliability, on the same site there are two gas turbines and two air separation units, which are substantially identical, producing both impure oxygen, needed for the gasification of fuels, and nitrogen. Each separation unit is fed from a gas turbine compressor and sends nitrogen only to this same gas turbine.
It is one object of the invention to remedy the defects of the known systems.
In particular, one object of the invention is to allow greater flexibility in the choice of products coming from an integrated air-separation/gas-turbine system. According to one aspect of the invention, this provides an integrated air-separation process producing an oxygen-enriched fluid and, optionally, a nitrogen-enriched fluid in a plant comprising at least two air separation units, each comprising at least two distillation columns, a first air compressor, a first combustion chamber and a first expansion turbine, in which process compressed air is delivered to the first air separation unit at least by the first air compressor which also delivers compressed air to the first combustion chamber, compressed air is delivered to the second air separation unit at least by an auxiliary compressor, the second separation unit:
i) not receiving air from a compressor which feeds a combustion chamber or
ii) receiving air which it treats by means of at least one compressor which also feeds a combustion chamber, the percentage of total air, treated in the second unit, which comes from the compressor feeding a combustion chamber, being less than the percentage of air, treated in the first unit, coming from the first air compressor (or coming from the first air compressor and a second air compressor also feeding a second combustion chamber), a nitrogen-enriched gas is sent from the first air separation unit upstream of at least one expansion turbine fed with combustion gases from at least one of the combustion chambers and optionally a nitrogen-enriched gas is sent from the second air separation unit upstream of at least one expansion turbine fed with combustion gases from at least one of the combustion chambers.
Preferably, the percentage of the total air, treated in the second unit, which comes from the compressor feeding a combustion chamber represents at most 80%, or at most 50% or even at most 30% of the percentage of air, treated in the first unit, coming from the first air compressor (or coming from the first air compressor and from a second air compressor which also feeds a second combustion chamber).
In certain methods of implementing the invention, an oxygen-enriched gas is sent from the first unit and/or the second unit to a gasifier or several gasifiers. This or these gasifiers deliver fuel to the combustion chamber (combustion chambers).
According to optional aspects of the invention:
the nitrogen-enriched gas coming from the first air separation unit is sent upstream of the first expansion turbine fed with combustion gases from a combustion chamber and a nitrogen-enriched gas sent from the second air separation unit is sent upstream of at least one expansion turbine fed with combustion gases from at least one combustion chamber, optionally the first turbine;
the percentage of cryogenic liquid produced as final product by the second unit with respect to the flow of air treated by the second unit is greater than the percentage of cryogenic liquid produced as final product by the first unit with respect to the flow of air treated by the first unit, or in which the second unit produces cryogenic liquid while the first unit produces none. For example, the second unit may produce a liquid richer in oxygen and/or a liquid richer in nitrogen and/or a liquid richer in argon than air;
the second air separation unit receives at most 50%, optionally at most 30%, of the compressed air which it treats from one or more compressors feeding one or more combustion chambers with compressed air, optionally the first compressor;
the first air separation unit is fed with air from a second air compressor which also feeds a second combustion chamber, the combustion gases from the second combustion chamber being sent to a second expansion turbine;
the first separation unit produces one or more oxygen-enriched fluids, this fluid containing at most 98 mol % oxygen and/or at least 80% of these products consisting of a fluid containing at most 98 mol % oxygen, preferably at most 97 mol %;
the first separation unit produces oxygen-enriched products, at least 90% of these oxygen-enriched fluids consisting of one or more fluids containing at most 98 mol % oxygen;
the second separation unit produces one or more oxygen-enriched fluids, this fluid containing at least 98 mol % oxygen or at least 50% of these oxygen-enriched fluids consisting of one or more fluids containing at least 98 mol % oxygen;
the first separation unit produces oxygen-enriched products, at least 70% of these products consisting of a fluid containing at least 98 mol % oxygen;
the first air separation unit is also fed with compressed air by a compressor which does not feed a combustion chamber and/or which feeds only the first air separation unit;
the second air separation unit is fed with compressed air by a compressor which does not feed a combustion chamber and/or which feeds only the second air separation unit;
the second air separation unit produces an argon-enriched final product;
only the second air separation unit produces an argon-enriched final product or in which the second air separation unit produces more argon-enriched final product(s) than the first unit;
the first air separation unit comprises a blowing turbine and/or the second air separation unit comprises a Claude turbine;
a compressor feeds both air separation units and does not feed a combustion chamber;
the first unit and/or the second unit comprise/comprises a low-pressure column from which an oxygen-enriched product fluid is derived, this low-pressure column operating at at least 1.3 bara, optionally at least 3 bara;
the first and/or second unit comprises a low-pressure column and a high-pressure column, and optionally a column operating at intermediate pressure between the low and high pressures;
the air sent from the first compressor to the first and/or the second air separation unit is compressed or expanded and/or the air sent from the second compressor to the first and/or second air separation unit is compressed or expanded.
According to another aspect of the invention, this provides an integrated plant comprising a first air separation unit, a second air separation unit, a first compressor, a combustion chamber, an expansion turbine, an auxiliary compressor, means for sending air from the first compressor to the combustion chamber and to the first air separation unit, means for sending air from the auxiliary compressor to the second separation unit and no means for sending air from the first compressor or another compressor associated with a combustion chamber to the second air separation unit.
Preferably, the plant comprises means for sending a nitrogen-enriched gas from the first separation unit upstream of the expansion turbine and/or means for sending a nitrogen-enriched gas from the second separation unit upstream of the expansion turbine and/or means for sending an oxygen-enriched gas from the first unit and/or from the second unit to one or more gasifiers which delivers or deliver fuel for (at least) one (the) combustion chamber.
According to other aspects of the invention, the plant may comprise:
means for sending air from the dedicated compressor to the first unit;
the first unit does not include a means of producing liquid as final product and/or the second unit does include a means of producing liquid as final product;
the first unit does not include an argon production column and/or the second unit does include an argon production column;
the first unit includes a blowing turbine and/or the second unit includes a Claude turbine and optionally does not include a blowing turbine.
According to another aspect of the invention, this provides an integrated air separation process producing an oxygen-enriched fluid and optionally a nitrogen-enriched fluid in a plant comprising at least two air separation units, each comprising at least two distillation columns, a first air compressor, a first combustion chamber and a first expansion turbine, in which process compressed air is delivered to the first air separation unit at least by the first air compressor, which also delivers compressed air to the first combustion chamber, compressed air is delivered to the second air separation unit at least by an auxiliary compressor which does not feed a combustion chamber but which also feeds the first air separation unit.
According to another aspect of the invention, this provides an integrated plant comprising a first air separation unit, a second air separation unit, a first compressor, a combustion chamber, an expansion turbine, an auxiliary compressor, means for sending air from the first compressor to the combustion chamber and to the first air separation unit, means for sending air from the auxiliary compressor to the first air separation unit and to the second air separation unit, this auxiliary compressor not feeding a combustion chamber.
Preferably, the auxiliary compressor is not connected with a unit which consumes compressed air, apart from the first and second air separation units.
Thus, the first air separation unit receives proportionally more air from a gas turbine than the second air separation unit. This second unit may even not be integrated at all with a gas turbine or else it may produce a nitrogen-enriched stream which is sent to the gas turbine.
Thus, the first air separation unit receives more air from a gas turbine than the second air separation unit. This second unit, which may even not be integrated at all with a gas turbine.
The degree of integration determines what products may be output by each unit, in general the products purest in oxygen and/or in argon coming from the second unit, the operation of which will be more stable, thanks to the low degree of integration.